1. Technical Field
The present invention relates to an electrophoretic display apparatus and an electronics device.
2. Related Art
With respect to electrophoretic display apparatuses each having a function of displaying color images, heretofore, an electrophoretic display element enveloping therein three kinds of particles, i.e., white color ones, black color ones and another color ones, has been proposed. In such an electrophoretic display element, individual particles are sorted into positively charged particles, negatively charged particles and non-charged particles. At the side of an active matrix substrate for driving the display elements, each pixel is provided with two pixel electrodes. Further, on an opposite substrate, a common electrode that is common to all pixels is provided.
Once both of the two pixel electrodes on the active matrix substrate and the common electrode are supplied with a positive electric potential and a negative electric potential, negatively charged particles and positively charged particles are attracted to the active matrix substrate side and the common electrode side, respectively. Therefore, users view a color tone created by the positively charged particles.
Further, once the two pixel electrodes on the active matrix substrate are supplied with a positive electric potential and a negative electric potential, respectively, and the common electrode is supplied with an intermediate electric potential therebetween (for example, a ground electric potential), both of the positively charged particles and the negatively charged particles are attracted to the active-matrix substrate side owing to electric fields arising from the two pixel electrodes. Therefore, users view a color tone created by the none-charged particles (refer to JP-A-2009-9092 and JP-A-2009-98382).
Here, in order to obtain the color tone created by the non-charged particles, it is necessary to cause electric fields to arise uniformly throughout the whole area of each pixel so that all of the positively charged particles and the negatively charged particles can be attracted to the active matrix substrate side. In order to realize this condition, a configuration resulting from combining and allocating comb-teeth shaped pixel electrodes is used in lots of cases.
However, supplying respective adjacent pixel electrodes with mutually different electric potentials results in occurrence of leakage current between the pixel electrodes via an electrophoretic layer. This leakage current flows between the two pixel electrodes, and thus, an amount of leakage current becomes larger in proportion to the length of a boundary between the two pixel electrodes. Therefore, in the case of the comb-teeth shaped pixel electrodes, a large amount of leakage current flows. Furthermore, the occurrence of leakage current leads to an increase of power consumption of an electrophoretic display panel.
Moreover, owing to such leakage current, there is a possibility of causing an electrochemical reaction between the electrophoretic layer and each of the pixel electrodes. Namely, there is a possibility of detracting reliability of the pixel electrodes. That is, there is a high possibility of occurrence of ionic migrations and/or corrode. If a precious metal, such as gold or platinum, is used as a material of the pixel electrodes, the reliability is enhanced; however, the use of such a material leads to an increase of cost and a growth of complexity of manufacturing processes thereof. Therefore, it has been difficult to enhance the reliability, and concurrently therewith, suppress increase of the cost. Consequently, in order to reduce an amount of such leakage current, a method for reducing the length of a boundary between the mutually adjacent pixel electrodes by enlarging a width of each of branch portions of the comb-teeth shaped pixel electrodes and/or enlarging each distance between the mutually adjacent two pixel electrodes can be conceived.
However, depending on the width of each of the pixel electrodes and the distance between the mutually adjacent two pixel electrodes, a problem in that there occur areas that are not subjected to any electric fields occurs, and as a result, particles existing at the common pixel side cannot be attracted. This phenomenon remarkably occurs in edge portions of each pixel area. Namely, particles distributed immediately above any one of branch portions located at the middle side of each pixel area are attracted by actions of electric fields arising from either of branch portions of a different pixel electrode, which are located at respective both sides of the branch portion located at the middle side thereof; however, each of branch portions located at respective peripheral edge portions of the pixel area is subjected to actions of electric fields arising from only one branch portion of a different pixel electrode, which is located at one side of and adjacent to the branch portion located at the peripheral edge portion thereof. Therefore, as a result, such a phenomenon causes a problem in that particles located at peripheral edge portions of the pixel area cannot be attracted.
Unintentional particles remaining at the common electrode side results in occurrence of unevenness of display.